The present invention relates to a highly electronically conductive composition which is graphite-based. More particularly, it relates to a graphite intercalation compound which is capable of conductivities approximating and even exceeding those attributed to pure copper.
Its utilities are widespread and many practical applications of the present compositions will be readily apparent to those skilled in the art. Foremost among these are formation of filaments of the composition for use as electrically conductive wires. In addition, the nature of the composition readily enables it to be formed into strips for use as bus bars in electrical equipment. The composition may also be formed into a metal composite and can hence be soldered or wrapped. Such composites are also useful in situations where physical strength is required in addition to high conductivity.
It has long been known that the unique crystalline structure of graphite makes it anisotropic with respect to conducting electrons. Its structure basically comprises planes of aromatically bound carbon atoms. Hence, each of such planes has .pi. clouds of electrons above and below it. These electron clouds have been said to contribute to its anisotropic conductive behavior, the conductivity being in a direction parallel to the aromatic carbon planes. This conductivity is approximately 5% that of copper.
Prior to the present invention, it was known that certain elements or molecules, when diffused into the graphite lattice, assume positions interstitial to the aromatic planes and improve graphite conductivity. Ubbeholde, for example, found that the interstitial compound formed between graphite and the Bronsted acid, nitric acid, has a conductivity almost equal to that of copper (0.6.times.10.sup.6 ohms cm.sup.-1) when measured parallel to the aromatic planes (A. R. Ubbeholde, Proc. Roy. Soc., A304, 25 1968).
U.S. Pat. No. 3,409,563 granted to F. Olstowski describes conductive graphite structures formulated from vermicular graphite and bromine, sulfur trioxide, and certain metal chlorides. The treated vermicular graphite is then compressed into high density structures.
The present invention differs markedly from previous graphite intercalation compounds in many respects. Unlike the Ubbeholde compound, it is not solely derived from nitric acid and has a greatly increased conductivity over the Ubbeholde material. Nor is the present invention necessarily made from graphite which has been exfoliated at high temperatures as described by Olstowski.